Uzay Mühendisliği

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http://hdl.handle.net/11527/25890

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  • Öge
    Attitude filtering with uncertain process and measurement noise covariance using SVD-aided adaptive UKF
    (Wiley, 2023) Hajiyev, Chingiz ; Cilden-Guler, Demet ; orcid.org/0000-0003-4115-341X ; orcid.org/0000-0002-3924-5422 ; Uzay Mühendisliği
    It is presented in this article how to simultaneously alter the process and measurement noise covariance matrices for nontraditional attitude filtering technique. The unscented Kalman filter (UKF) and singular value decomposition (SVD) methods are integrated in the nontraditional attitude filtering algorithm to estimate a nanosatellite's attitude with an inherent robustness feature. The SVD approach determines the attitude of the nanosatellite and provides one estimate at a single frame utilizing measurements from the magnetometer and Sun sensor as the initial stage of the algorithm. These attitude terms are subsequently fed into the UKF with their error covariances, which makes the filter robust inherently. The attitude estimations of the satellite are compared between the filters presented. The Q (process noise covariance) adaption approach with multiple scale factors is specifically suggested for differences in between the process channels. Performance of the multiple scale factors-based adaptive SVD-aided UKF is examined in the event of process noise increase, which may result from changes in the environment or satellite dynamics.
  • Öge
    Adaptive fault-tolerant multiplicative attitude filtering for small satellites
    (Wiley, 2024) Kınataş, Hasan ; Hajiyev, Chingiz ; orcid.org/0000-0003-2089-223X ; orcid.org/0000-0003-4115-341X ; Uzay Mühendisliği
    This study tackles the problem of fault-tolerant attitude estimation for small satellites. A probabilistic adaptive technique is presented for the multiplicative extended Kalman filter (MEKF) algorithm that is used in attitude estimation. The presented method is based on tracking the normalized measurement innovations in the filter and calculating the probability of the normal operation of the estimation system. Using this probability, the filter gain is corrected to maintain the tracking performance of the filter despite faulty measurements. In order to evaluate the performance of this method, several simulations are performed where different types of faults are introduced to the synthetic attitude sensor measurements (magnetometer and sun sensor) at different times. Simulation results are compared not only with a conventional EKF but also with another popular adaptive Kalman filter, an adaptive Kalman filter with multiple scaling factors (MSFs).
  • Öge
    Investigation of the coupling between the dynamics of vortical structures and flame stability in bluff-body premixed combustion using extended spectral proper orthogonal decomposition
    (ASME, 2025) Khalifehei, Morteza ; Yalçınkaya, Yağız ; Padilla-Montero, Iván ; Güngör, Ayşe Gül ; Rodríguez, Daniel ; Uzay Mühendisliği
    Large eddy simulation data of a bluff-body stabilized flame are analyzed using spectral proper orthogonal decomposition (SPOD) to investigate: (i) the role of flame-vortex interactions in the dominant flow dynamics and (ii) how the proper choice of the cross-spectral density (CSD) defining SPOD can assist in identifying the underlying dynamics. Bluff-body flame holders aim to achieve stable flames under lean premixed conditions to minimize pollutant emissions. The recirculation region induced by the body promotes the mixing of hot combustion products with unburnt gases, preventing the global blowoff. However, the coupling between the shear layers and flame-induced vorticity sources can result in large flow structures that either contribute to increased flame stability or exhibit features typical of the early stages of flame blowout. SPOD is a data-driven technique remarkably powerful in extracting low-dimensional models. For each frequency, it computes a basis of orthogonal modes that maximizes the content of a predefined CSD in the leading modes. By choosing physically relevant variables to construct the CSD, different physics can be explored, which is used here to investigate the coupled dynamics between the flame-induced baroclinic torque, vortical structures, and the temperature field. The results show that the vorticity and temperature fields exhibit low-dimensional dynamics characterized by a narrowband frequency and its harmonics; these dynamics are varicose oscillations of the flame region, governed by the baroclinic torque. Sinuous oscillations typical of wake instability for nonreactive flows are also present, suggesting a competition between them.